Simplistically, the word “mathematics” can be defined as “instruction subject”. It is based on an ancient Greek word, máthēma, which meant “that which is learnt”. Plato defined it as “discipline, doctrina, cognition, ars”. Many have agreed that this can be taken to mean “learning”, and “anything we aim to know”. In Hermann Bonitz’s Index Aristotelicus, the term “doctrina mathematica” is used which indicates a more specific meaning of the term; in effect, Aristotle was restricting it to referring to mathematical science. Within the same generation, two Greek philosophers narrowed the term to what would become recognized as mathematics today.
This narrowing of the term may be explained by the growth in emphasis and importance of the education in and philosophy of that the Greeks placed on four scientific disciplines – music, astronomy, geometry and arithmetic – that were looked upon as being mathematical. They were seen to be a natural grouping and by the Middle Ages became the Quadrivium.
For many centuries, the word mathematics was used more specifically for astronomy but its use as the word we know today (which essentially comes from the Greek plural form of máthēma, i.e. la mathēmatiká) began after 1500 a.d. but more specifically after 1700 a.d.
Now we simply call it math!